Extraction of Metals from their Ores

Ores and Minerals

An ore is a naturally occurring rock or sediment that contains sufficiently high amounts of metals that the extraction of the metal is economically feasible.
Minerals are the natural substances in which the metals and their compounds are found in the earth.
The metals and metal compounds found in ores are often in the form of oxides, sulphides, and carbonates.

Concentration of Ores

Concentration of ores, or ore dressing, involves converting bigger lumps of ore into smaller pieces which are more suitable for extraction.
This process mainly consists of crushing and grinding followed by physical or chemical methods like washing, magnetic separation, froth floatation, or leaching.
The choice of method for concentration depends on the nature of the ore.

Extraction Methods Based on Reactivity

Metals that are less reactive, such as gold, can simply be heated as they do not react with the substances in their ores.
Metals like copper, zinc, or lead, which are moderately reactive, can be extracted from their ores by heating them with carbon or carbon monoxide. This is known as reduction with carbon.
For highly reactive metals like sodium, calcium, aluminium, and potassium, extraction of metal from the ore involves electrochemical methods. This process is termed as electrolysis.

Electrolysis in Metal Extraction

The process of electrolysis involves passing an electric current through an ionic substance that is either molten or in solution. This causes the substance to break down into constituent elements.
For example, aluminium is extracted from its ore (bauxite) using electrolysis. The ore is first treated to form aluminium oxide, and then this oxide is dissolved in molten cryolite.
Aluminium forms at the cathode, where reduction takes place, and oxygen forms at the anode, where oxidation takes place.

Extraction of Iron

For the extraction of iron from its ore (haematite), the ore is mixed with coke and limestone and then heated in a blast furnace.
The red-hot iron ore is then reduced by the carbon monoxide gas, forming solid iron and carbon dioxide.
The limestone helps to remove impurities in the iron ore and forms a waste product called slag, which can be removed later.

Purification of Metals

Extracted metals often contain impurities that must be removed in a process called refining.
One common method is electrolytic refining, where the impure metal is made the anode and a strip of pure metal is made the cathode.
Upon electrolysing, the pure metal is deposited on the cathode, while the impurities fall off from the anode and settle down, known as anode mud.